Arrangement for mixing two frequencies in a superheterodyne receiver



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I July 2, 1940. R. BARTHELEMY ARRAHGEIENT FOR HIKING TWO FREQUENCIES INA SUPERHETERODYNE RECEIVER Filed Nov. 24, 1936 UJT/LLATOR ATTORNEYPatented July 2, 1940 UNITED STATES PATENT OFFICE ARRANGEMENT FOR MIXINGTWO FRE- QUENCIES IN A SUPERHETERODYNE RE- CEIVER Application November24, 1936, Serial No. 112,459 In Germany January 27, 1936 4 Claims.

The present invention relates broadly to modulation circuits and moreparticularly to frequency combining circuits.

Superheterodyne receivers require mixing arrangements permitting twofrequencies to be so superimposed that a desired third frequency isthereby produced. A great number of special circuits serving for thisend are already known, the modern methods operating exclusively withelectron tubes.

The present invention relates to a novel method in which aphoto-electric cell plays the part of a frequency combining or mixertube.

In a photo-cell to which a potential is applied, it is known thatcurrent can pass through it only when quantities of light impinging onthe cathode, release electrons whereby the emission of thecathode ismade possible. Therefore, the photo-current produced can be controlledby the intensity of the impinging light.

In accordance with the present invention, a photo-cell is inserted intothe high-frequency receiver circuit tuned to the frequency 11. When thephoto-cathode is" exposed to the radiations of a light ray of constantintensity the photo-cell acts as a detector and the high-frequency, asis known wlll be detected in the cell, and thus represents anintermittent current of constant value. But if the intensity of thelight source-for instance as when the light source is fed by a secondhigh-frequency fz-is likewise subject to periodic variations, thefrequencies 11 and I: will be superposed on each other. The desiredintermediate frequency can then be filtered out from the resultantphoto-current by means of any suitable resonance circuit.

An application of the invention is shown in the single figure of thedrawing-which illustrates schematically a portion of a receiverutilizing the features of the present invention. The arrivinghigh-frequency is herein supplied from an antenna I to a tuning circuit3, 4. The high-frequency potential appearing in said circuit isapplied'to a photo-cell P illuminated by a light source M which may be aglow tube. Light source M is energized by energy generated by a localoscillator 5. Hence, the light intensity of the source M varies inaccordance with the frequency of the oscillations generated by theoscillator 5".SiDC8 the incoming signal oscillations and the localoscillations are both effectively impressed upon the photo-electric cellP, it follows that one of the products of the output of thephoto-electric cell will be intermediate frequency energyresulting fromthe combination of the signal oscillations and the local oscillations.The desired intermediate frequency energy may be selected out of thephoto-electric cell output by the coupled tuned circuits 6, 1 and 8, 9and fed to any suitable intermediate frequency utilizing device whichmay be connected across terminals 10 and II. To receive signals from astation operating on another wave length, the input circuit 3, 4 istuned to the new wave length and the frequency of the oscillationsgenerated by oscillator 5 is changed so that the same intermediatefrequency will be available across terminals i and l l as is commonpractice with superheterodyne receivers. The oscillation generator hasnot been shown in detail since any of the well known types ofoscillation generating arrangements may be utilized for this purpose.

If however, a relaxation oscillation generator is to be employed, theglow tube thereby used may serve as the light source for illuminatingthe photo-cell.

One type of relaxation oscillation generator which may be used is shownin U. S. Patent 1,927,425. Another type is shown in U. S. patentapplication Serial No. 748,773 filed October 10, 1934, by J. P. Smith.

Besides the example referred to, the invention can be utilized innumerous modulation circuits of other types. As compared with the knownmodulation methods. the greatest advantage of the present invention willlie in the complete de-coupling of the oscillator thereby excluding areaction upon the preliminary circuits.

What I claim is:

1. In a superheterodyne receiver, a frequency changer circuit forproducing intermediate frequency energy from received radio frequencysignal modulated carrier energy comprising. in combination, aphoto-electric cell having an electron emitting element, means includinga source of light energy for energizing said electron emitting element,and means comprising a local oscillation generator device forperiodically varying the intensity of said light energy at a frequencywhich when combined with energy of the frequency of said received radiofrequency modulated carrier energy produces the desired intermediatefrequency.

2. In a superheterodyne receiver, a frequency changer circuit forproducing desired intermediate frequency energy by combining receivedradio frequency signal modulated carrier energy with locally producedenergy of a predetermined frequency comprising, in combination, aphotoelectric cell having a light controlled electron emitting element,a light source for applying light energy to said electron emittingelement, an input circuit and an output circuit for said photo-electriccell, means for applying the received signal modulated carrier energy tosaid input circuit, an intermediate frequency resonant circuit includedin said output circuit, energizing means for said light sourcecomprising an oscillation generator for periodically varying theintensity of the light energy at a frequency which when combined withthe radio frequency signal modulated energy produces energy ofintermediate frequency, and a utilizing circuit coupled to saidintermediate frequency resonant circuit.

3. In a receiving system for high frequency electric waves, a mixercircuit having an input circuit tunable over a range of signalfrequencies and an output circuit resonant to an intermediate frequency,said mixer circuit including a. photo-electric cell connectedintermediate the input and output circuits, a source of light for saidphoto-electric cell comprising a glow tube and means for periodicallyvarying the intensity of the light from the glow tube at a frequencywhich when combined with the frequency to which the input circuit istuned produces the intermediate frequency to which the output circuit istuned, said last named means comprising an oscillation generator forsupplying the glow tube with energizing current.

4. In an arrangement for obtaining a third frequency by combining afirst frequency and a second frequency, a. photo-electric cell having anoutput circuit resonant to said third frequency, and an input circuit, asource of light for said photo-cell. means for impressing upon saidinput circuit a voltage of said first frequency whereby said voltage isimpressed across the photo-cell, and means for varying the intensity oflight from said source of light at said second frequency.

